Loughrey, 44, and his son, Craig Loughrey, returned to the truck, where Loughrey secured his son in a booster seat on the passenger side. He then placed the long gun in the bed of the truck.

As he got into the truck, he reached to place the handgun into a glove box storage unit, police told the Tribune-Review. That's when it fired.

Authorities were called at 10:53 a.m. local time and found the boy lying next to the truck after a failed attempt at resuscitation. They stayed on scene until after 1 p.m., dispatchers said.

"All evidence at this point would suggest that this incident is accidental," the Pennsylvania State Police report stated.

According to the Tribune-Review, Loughrey didn't realize that a round remained in the gun's chamber.

“This happens all too often where people think the gun was empty,” State Police Lt. Eric Hermick.

Twig’s Reloading Den is an outdoor supply store about 70 miles from Pittsburgh.

Imy Howard, owner of Howard & Son Meat Packing store next door, told the Pittsburgh Post-Gazette that her son heard a shot this morning. She said that Twig’s Reloading Den hosted target shooting in the back parking lot last week but not this week.

A Twig’s employee told the Post-Gazette that the incident was “just an unfortunate accident.”